I personally prefer AMOLAD to BNW, although if you had asked me a few years ago, I'd probably have told you the opposite.
The problem is with BNW, actually. It has lost much of its initial appeal to me. Although I still enjoy listening to it, I can surely say that the individual songs on BNW are weaker than the ones on AMOLAD taken out of the context of the album.
BNW suffers from lack of idea behind it, I would say. I don't mean that every album should be conceptual, but in my opinion the best Maiden albums are at least loosely centred around an idea - SIT, SSOASS, The Final Frintier and AMOLAD. BNW seems like a random collection of songs thrown in.
AMOLAD, on the other hand is extremely consistent - both in terms of songwriting quality and in terms of concept and imagery. It feels like an entity.
EDIT: Morning, Moon Child!
Another EDIT: Bugger! I have 40 minutes, I won't be able to finish my wok.